This invention relates to a cooling structure for a mower supply device and, especially, to a cooling structure of a power supply device including semiconductor devices which generate much heat and need forced cooling, and circuit components which have poor heat resistance.
It has recently become common to include an invertor circuit in a power supply device used for such purpose as power failure protection, communication or discharge lamp lighting. Power semiconductor devices which are liable to generate Joule's heat are used in such invertor circuits. Moreover, the number of components including the semiconductor devices increases with a trend of multiplication of the invertor circuit and increase in its switching frequency. On the other hand, it becomes necessary to reduce the size of the device and consequently arrange the components in higher density to accommodate a demand for portability of the power supply device. As a result, the power supply device suffers from increased generation of internal heat as lowering of component cooling power and, thus, it is necessary to provide forced cooling means of high cooling power.
Therefore, the inventors of this application have proposed a power supply device provided with such a forced cooling device as disclosed in the Japanese opened patent gazette No. H5(93)-85092. In this device, as shown in FIG. 1, a housing 1 thereof is divided into upper and lower chambers 3 and 4 by a partition wall 2, and air inlet and outlet openings 7 and 8 are formed in side walls 5 and 6 of the upper chamber 3. A ventilating fan 9 is attached inside the air outlet opening 8 in order to forcedly form an air flow from the inlet opening 7 to the outlet opening 8. A cooling fin structure 10 is attached to the partition wall 2 and heat generating power semiconductor devices 11 selected from the power supply circuit are attached onto the fin structure 10. Accordingly, the air coming in from the inlet opening 7 passes as shown over the semiconductor devices 11 and between cooling fins 12 of the fin structure 10 to the outlet opening 8, thereby cooling the semiconductor devices 11. On the other hand, such comcomponents as a battery, capacitor and printed circuit board, which are selected from the power supply circuit components other than the semiconductor devices 11 and which generate no heat by themselves but together cause a slightly rising temperature, are disposed in the lower chamber 4. Thus, the components 13 are separated from the heat generating semiconductor devices 11 and maintained at an acceptable operating temperature in the lower chamber 4.
However, the internal temperature of the lower chamber 4 may increase gradually due to accumulation of heat conducted through the cooling fin structure 10 and partition wall 2, and a little heat generated by the components 13 by themselves, and exceed the threshold temperature of the components 13. Therefore, it is necessary to provide the components 13 in the lower chamber 4 with cooling means as well. However, even if the lower chamber 4 is provided with a ventilation opening for natural cooling through convection, its effect will be small. Also, it is undesirable to provide a ventilation fan in the lower chamber 4 in addition to the upper chamber since this results in an increase both in the size and cost of the device.